Ozonation of the food dye Brilliant Blue in aqueous medium: monitoring and characterization of products by direct infusion electrospray ionization coupled to high-resolution mass spectrometry

Colorimetry Combined with Inner Filter Effect-Based Fluorometry: A Versatile and Robust Strategy for Multimode Visualization of Food Dyes

Herein, a strategy combining colorimetry and inner filter effect (IFE)-based fluorometry was developed for multimode visualization of food dyes (FDs) using CdTe quantum-dots-doped fluorescent indicator papers as a sample-to-answer device. Colorimetry was straightforwardly achieved by FDs extraction through electrostatic interaction and hydrophobic effect while fluorometry was implemented by IFE-induced fluorescence quenching. RGB/gray-scale values of colorimetry and fluorometry were furtherly picked by a smartphone application and applied to reconstruct color information-based digital image analysis for both direct alignments and linear regression analysis. The apparent color and fluorescence of FDs-bound indicator papers, together with their digitized color information, showed a good mapping to FDs concentrations in the range of 0-0.5 mg/mL for Sunset Yellow, 0-0.2 mg/mL for Allura Red, and 0-0.08 mg/mL for Brilliant Blue. As a proof of concept, the dosages of these FDs in real beverages and simulated dye effluents were deduced and cross-validated by different visualization modes, and finally double-checked by instrumental techniques such as spectrometric methods, high-performance liquid chromatography (HPLC), and mass spectroscopy (MS). The above findings concluded that (i) IFE mechanism is generally applicable to build fluorometric systems and (ii) cross validation of different visualization modes can markedly improve detection accuracy, which may provide references for design and fabrication of novel "lab-on-paper" devices for visualization applications with high reliability.

Understanding the performance of a paper-based UV exposure sensor: The photodegradation mechanism of brilliant blue FCF in the presence of TiO2 photocatalysts in both the solid state and solution

RATIONALE

The decolouration of brilliant blue FCF by the action of titanium dioxide (TiO₂ ) under ultraviolet (UV) exposure has been recently reported as the basis of a paper-based sensor for monitoring UV sun exposure. The mechanism of brilliant blue FCF photodegradation in the presence of the photocatalyst and the resulting photoproducts are thus far unknown.

METHODS

The UV-initiated photodegradation of brilliant blue FCF in the presence of TiO₂ for both the aqueous and the solid state was investigated. Degradation in the solid state was observed using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-MS). Decomposition of the dye in the aqueous state was analyzed using liquid chromatography/mass spectrometry (LC/MS) and ultraviolet-visible (UV-Vis) spectroscopy.

RESULTS

After UV radiation exposure, the brilliant blue FCF base peak [M1 + NH₄ ]⁺ (m/z calc. 766.194 found 766.194) decreased in the LC/MS chromatogram with a concomitant appearance of BB-FCF decomposition products involving the sequential loss of the N-ethyl and N-methylbenzene sulfonate (MBSA) groups, assigned as [M2 + H]⁺ (-MBSA, calc. 579.163 found 579.162), [M3 + H]⁺ (-MBSA, -Et, calc. 551.131 found 551.131), [M4 + H]⁺ (-2MBSA, calc. 409.158 found 409.158), [M5 + H]⁺ (-2MBSA, -Et, calc. 381.127 found 381.127). Ions [M2 + H]⁺ and [M3 + H]⁺ were also identified in the photodegradation products using MALDI-MS. Observation by UV-Vis indicated a decrease in the solution absorbance maxima and an associated blue-shift upon UV exposure in solution.

CONCLUSIONS

The LC/MS analysis indicated two main oxidation processes. The most obvious was attack of the N-methylene, eliminating either ethyl or MBSA groups. The presence of the hydroxylated decomposition product M13 ([M13 + H]⁺ , calc. 595.157 found 595.157) supported this assignment. In addition, the detection of photoproduct M8, proposed to be 3-((ethylamino)methyl)benzenesulfonic acid ([M8 + H]⁺ , calc. 216.069 found 216.069), indicates an aryl-oxidative elimination. The absence of the aryl-hydroxy products normally expected to accompany the formation of M8 is proposed to be due to TiO₂ -binding catechol-like derivatives, which are then removed upon filtration.